Can't get boolean to work

Well I just learned of the lovely boolean and gave it a shot, it froze my computer, a 512 stick later and it doesn’t freeze, but it doesn’t work either. Whenever I try the difference I get nothing or sometimes it will pop up with “both meshes must be a closed mesh” I have no clue what that means. Any advice or maybe a point towards a good tut?

it means that there musn’t be any holes in the mesh. Say you have a sphere, and delete one of the faces, then it won’t be a closed mesh. However… if you need it to look like there is a hole in it, try extruding everything in a little bit, then it should be closed